The electrical-power saving functions by microcontroller can be realized by following two ways. The first way is an idle mode, wherein the microcontroller is in an idle (without working) state while the devices connecting with the microcontroller (such as oscillators, counters, or serial interrupt unit) remain functioning. In this idle mode operation, the operating current for microcontroller is about 1 mA.
Another way for saving electrical-power is power down mode, wherein the oscillator and the microcontroller are both in off state. In this power-down mode, the operating current for microcontroller is below 10 uA.
The microcontroller is generally designed to switch from normal state to a power-saving state when the external devices connected to the microcontroller are idle for a specific period. At the power-saving state, the microcontroller is in an off state and can not function. The conventional device is designed to trigger the microcontroller to a workable state by a power switch. However, the operating current for the microcontroller triggered by the power switch is about 200.about.400 uA. The current consumption is excessively large.